71 Phenological Characterization of Mendoza (Argentina) Olive (Olea europaea L.) Germplasm E.R. Trentacoste and C.M. Puertas INTA EEA Junín, Mendoza Argentina Keywords: flowering, maturity, olive accessions, risk frost, thermal time Abstract The phenological characterization of the olive tree for a specific location is needed to improve the crop efficiency and know the adaptation of new cultivars. The aim of this work was to estimate the occurrence of the olive germplasm flowering and maturity in Mendoza province, using a thermal model. During six seasons and using 59 olive accessions, the day of full bloom (80% of the flowers opened around the canopy) and maturity (80% of the fruits at veraison around the canopy) was determined. The length of the phenological stages studied was expressed in thermal time using a model of thermal time and a base temperature = 8.5°C. The average of full bloom and maturity of the olive germplasm collection was 3 November (±9 days) and 28 April (±42 days), respectively. In order to flower, 80% of the accessions required between 420 and 520°C days (counted from 1 August) and the duration of the flowering-maturity stage showed great variability among the accessions, in the range between 1867-2287°C days. The frost risk during flowering was 0.5%, while 37 accessions showed a greater frost risk likelihood of 50% during the maturity of the fruits. The use of the thermal time had reduced the interannual variability in the estimation of the phenological stages by 30% compared to the method of number of days, and gave a better estimation of the development of different olive cultivars. INTRODUCTION In Mendoza, olive crop extends over 14,643 ha. In the last 5 years, olive production and surface have strongly increased and, as result, olive has become the second most important fruit crop after the grapevine. The phenological characterization of olive cultivars has several practical advantages: (i) cultivar classification according to the length of their cycle (Barranco et al., 1994, 1998), (ii) prediction of an insect attack or disease, thus making more efficient the phytosanitary control, (iii) crop management, i.e., water restrictions during specific phenological stages (Goldhamer, 1999), and (iv) cultivar adaptation to new regions (Ayerza and Sibbett, 2001). Most of previous studies related to the olive phenology have been focused on local prediction of the flowering (Barranco et al., 1994; Orlandi et al., 2002). The ripen period has received less attention (Barranco et al., 1994), even though it is essential in order to plan the harvest and obtain high quality products. Temperature has been described as the most important variable for the olive phenology, since it affects physiological processes of the plant (Moriondo et al., 2001; Orlandi et al., 2005); while the photoperiod seems to no significant effect on those processes (Hackett and Hartmann, 1964). The strong relationship between phenology stages and temperature has allowed that different thermal models (e.g., De Melo-Abreu et al., 2004; Orlandi et al., 2005) could predict the floral phenology in olive trees. The aim of this study was to estimate the occurrence of the olive germplasm collection stages of flowering and maturity in Mendoza province (Argentina), using a thermal sum model. MATERIALS AND METHODS The olive collection is located in the grounds of the Estación Experimental Agropecuaria Junín (INTA) (33°06’S; 68°26’W, 653 m a.s.l.), Mendoza province, Proc. VI th IS on Olive Growing Eds.: E.M. Sampaio and A.C. Pinheiro Acta Hort. 949, ISHS 2012